Removing copper-containing incrustations from steam generators



Patented Sept. 11, 1951 REMOVING COPPER-CONTAINING INCRUS- TATIONS FROM STEAM GENERATORS Francis N. Alquist, Joseph L. Wasco, and Carroll R.-Irons, Midland, Mich, assignors-to lhe Dow Chemical Company, Midland, -Mich., acorporation of Delaware No Drawing. Application-August 29, 1949, Serial No.'113,032

4 Claims.

The invention relates to methods of cleanin the internal ferrous metal surfaces of steam generating equipment. It more particularly concerns an improved method of removing certain incrustations from the internal ferrous metal surfaces of high pressure steam generating equipment Whichis operatedin connection with a condenser whose condensing surface is of copper alloy.

In the-operation of-high pressure steam generating equipment (over 600 pounds per square inch steam pressure) in which the feedwater is largely returned condensate from a copper alloy condenser, incrustations are usually produced upon the steam generating surfaces of the steam generator despite the fact that the feed water is substantially pure. These incrustations, we have found, oftentimes contain cop-per, both in metal- :lic form and combined with oxygen, corroded from the copper alloy condenser by the action of the condensed steam which carries the copper to the steam generator.

Attempts to remove such incrustations, as by the use of conventional acidizing procedures, are not Wholly successful. Tests have shown that by acidizing incrusted steam generating surfaces of the usual high pressure steam generator, having copper in the incrustation, some of the copper is removed from the incrustation and some of the copper so-removed is redeposited elsewhere on the surfaces of the steam generating equipment during the acidization so that only a partial net removal of copper from the incrusted surface results. Insofar as We are aware, there is no satisfactory method commercially available for treating the internal ferrous metal surfaces of high pressure steam generating equipment subject to deposition of copper containing incrustations so as to free the surfaces of the incrustations and the copper. Accordingly, it is an object of the invention to provide a method fulfilling this need. Other objects and advantages will become apparent as the description of the invention proceeds.

In order to achieve the objectives of the invention, we have found that a number of successive treatment steps must be applied to the ferrous metal surface from which the coppercontaining incrustation is to be removed. These steps are the following:

(a) The incrusted surface is first treated with an aqueous hydrochloric acid solution having an HCl content of 5 to 25 per cent as by filling the incrusted vessel with a sufficient volume of the acid solution to cover the incrustation. In very large vessels, the incrustations may be treated by directing a stream of the acid solution onto the incrustation instead of filling the vessel. If

desired, a corrosion inhibitor may be added to the acid solution to reduce the rate of attack upon the ferrous metal underlying the incrustation.

The speed of the action of the acid on the incrustation may be increased by raising the temperature'of the acid solution. A suitable temperature is about'1'50" F. although other temperatures may be used. Theacid is allowed to remain upon the incrustation preferably until the dissolving action substantially ceases. I'he spent solution is disposed of and the treated surface rinsed with water. lns'oine ins'tances, it 'is desirable to flush the "equipment with a strong flow of water, as when seaming or sloughing of the incrustations'occurs as -a result of the acid treatment.

(b) The acidi'zed and rinsed incrustation is treated with an aqueous ammoniaca1 oxidizing solution, such-as a'somtion in aqueous ammonia of "a strong oxidizingfagent e. g. sodium or potassium :chlorate or fpe'rsulfate, :pot'a'ssium :per-

.manganate, sodium chromate, hydrogen peroxide.

An ammonium salt is preferably also added to the solution, e. g. ammonium carbonate, ammonium sulfate. A procedure similar to that employed for the acid solution is used to brin the aqueous ammoniacal oxidizing solution into contact with the incrustation. This operation is carried out preferably at to F., although other temperatures may be used, and the solution is allowed to remain in contact with the incrustation preferably 3 to 6 hours or until the solution no longer gains in copper content. The following examples are illustrative of ammonia- After the copper in the incrustations has been dissolved, as indicated by the fact that the solution no longer increases in copper content, the resulting spent solution is removed from the equipment and the treated surfaces are rinsed with Water.

After rinsing off the spent ammoniacal oxidizing solution, the treated ferrous metal surface is again acidized using a dilute aqueous hydrochloric acid solution, such as one containing about 1 to 5 per cent of E01 by weight. This solution need not remain in contact with the surface to be treated for more than a few minutes. The spent acid solution is then removed.

((1) The surface, after acidizing the second time as in (c), is treated with a dilute aqueous alkaline solution such as soda ash, caustic soda, or trisodium phosphate, for example, dissolved in water in a concentration of about 1 per cent. The solution preferably is heated to boiling in the equipment for about 30 minutes befor discarding. The equipment thus treated is ready for service.

By the foregoing method, we have found that copper containing incrustations formed upon the steam generating surfaces in high pressure steam generating equipment using the condensed steam from copper alloy condensers as the feed water are completely removed leaving the surfaces clean.

We claim:

1. The method of removing copper-containing incrustations deposited upon the ferrous metal surface of high pressure steam generating equipment which comprises the steps carried out in the order stated of inundating th incrusted surface with an aqueous solution of hydrochloric acid containing 5 to 25 per cent of HCl and a1- lowing the acid to act upon the incrustations until the dissolving action has substantially ceased, removing the resulting spent acid from the acid treated incrustations, inundating the resulting acid treated incrustations with an aqueous ammoniacal solution of an oxidizing agent and allowing the solution to remain in contact with the incrustation until the solution no longer increases in copper content, removing the spent aqueous ammoniacal solution of the oxidizing agent from the treated ferrous metal surface and rinsing the same, inundating the rinsed surface with a dilute aqueous solution of hydrochloric acid, thereafter removing the solution, and then treating the resulting acid treated surface With a dilute aqueous alkaline solution.

2. The method according to claim 1 in which the aqueous ammoniacal solution of the oxidizing agent contains ammonium persulfate as the oxidizing agent.

3. The method according to claim 1 in which the aqueous ammoniacal solution of the oxidizing agent contains sodium chlorate as the oxidizing agent.

4. The method according to claim 1 in which th aqueous ammoniacal solution of the oxidizing agent contains hydrogen peroxide as the oxidizing agent.

FRANCIS N. ALQUIST. JOSEPH L. WASCO. CARROLL R. IRONS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,050,678 Moreno Jan. 14, 1913 1,816,881 Warnke Aug. 4, 1931 2,395,694 Spence Feb. 26, 1946 2,476,823 ONeil July 19, 1949 

1. THE METHOD OF REMOVING COPPER-CONTAINING INCRUSTATIONS DEPOSITED UPON THE FERROUS METAL SURFACE OF HIGH PRESSURE STEAM GENERATING EQUIPMENT WHICH COMPRISES THE STEPS CARRIED OUT IN THE ORDER STATED OF INUNDATING THE INCRUSTED SURFACE WITH AN AQUEOUS SOLUTON OF HYDROCHLORIC ACID CONTAINING 5 TO 25 PER CENT OF HC1 AND ALLOWING THE ACID TO ACT UPON THE INCRUSATIONS UNTIL THE DISSOLVING ACTION HAS SUBSTANTIALLY CEASED, REMOVING THE RESULTING SPENT ACID FROM THE ACID TREATED INCRUSTATIONS, INUNDATING THE RESULTING ACID TREATED INCRUSTATIONS WITH AN AQUEOUS AMMONIACAL SOLUTION OF AN OXIDIZING AGENT AND ALLOWING THE SOLUTION TO REMAIN IN CONTACT WITH THE INCRUSTATION UNTIL THE SOLUTION NO LONGER INCREASES IN COPPER CONTENT, REMOVING THE SPENT AQUEOUS AMMONIACAL SOLUTION OF THE OXIDIZING AGENT FROM THE TREATED FERROUS METAL SURFACE AND RINSING THE SAME, INUNDATING THE RINSED SURFACE WITH A DILUTE AQUEOUS SOLUTON OF HYDROCAHLORIC ACID, THEREAFTER REMOVING THE SOLUTION, AND THEN TREATING THE RESULTING ACID TREATED SURFACE WITH A DILUTE AQUEOUS ALKALINE SOLUTION. 